This invention relates to telephone systems and, in particular, to telephone systems which include a centrex telephone exchange having a multi-station pick-up capability for the telephone stations served by the exchange.
In centrex telephone exchanges, the management of telephone calls to and from the telephone stations served by exchange is computer processor controlled and driven. In one form of existing centrex exchange (i.e., the NTI DMS 100), the exchange provides a multi-station pick-up capability. In this type of exchange, the memory of the centrex is provided with a map which defines the other telephone stations of the exchange which can pick-up telephone calls originating at each particular station of the exchange. Each particular station thus defines with these other stations a so-called "multi-station pick-up group".
Hereinafter, when referring to the stations of a multi-station pick-up group, the term "primary station" shall be used to refer to the station whose call can be picked-up and the term "secondary station" shall be used to refer to each station which can pick-up for the primary station. Also, as can be apprecitated, any telephone station in the exchange might be a primary station of one pick-up group and a secondary station of one or more other pick-up groups.
When the centrex exchange originates a call at a primary station of a pick-up group, i.e., rings that station, and the primary station does not pick-up, any of the secondary stations in the pick-up group can then pick-up the call. Pick-up is initiated by a secondary station transmitting a pick-up signal to the centrex exchange. This pick-up signal is typically generated by preselected keying at the secondary station.
The centrex exchange receives the pick-up signal and processes the signal via its pick-up group map. In particular, the centrex determines from this map whether the secondary station identified by the pick-up signal is in the pick-up group of the called primary station. If the secondary station is in this pick-up group, the centrex then transfers the call from the called station to the secondary station and the call is then picked up.
In order for the secondary telephone stations in each pick-up group to be aware of the call status at the primary station of the group, each secondary station is provided with a lamp which identifies the primary station and whose state indicates the status of such station. Control of these lamps is through the centrex exchange.
More specifically, the centrex exchange monitors the status of the primary station in each pick-up group, and transmits to the secondary stations in the group lamp control signals which control the states of the lamps of the secondary stations in accordance with the monitored status (e.g., primary station busy--secondary station lamp is controlled to be full on; primary station ringing--secondary station lamp is controlled to be flashing at specified rate; etc.). Since, as above-indicated, any given station in the exchange may be a secondary station in more than one pick-up group, i.e., may be able to pick-up for several primary stations, each station of the exchange may have several lamps which have to be controlled. As a result, to accomodate the required lamping control, the processing load on the centrex is considerable. This tends to reduce the capacity of the exchange.
Also, in this existing type of centrex exchange, the design is such that the lamp control signals are coded (e.g. frequency-shift-key) analog signals. This necessitates the use of special coding equipment at the centrex for each telephone station and has limited use of the system to analog stations.
As can be appreciated, the above-described centrex exchange provides considerable flexibility in being able to establish and vary the multi-station pick-up groups, since this is readily accomplished simply by changing the pick-up group map in its memory. However, the need for lamping control through the centrex, the requirement for analog coding equipment and the confinement to analog telephone stations has made designers look to alternative types of systems which do not have these constraints.
One alternative type of system which has been designed (e.g., the system developed by David Systems Corporation) makes use of modular station controllers between the telephone stations and the centrex exchange. These station controllers are each assigned a number of stations and each permits digital communication with its assigned stations. Multi-station pick-up is accomplished by providing both lamping and switching control for the pick-up groups at the controllers. Switching equipment is, therefore, needed at each controller to permit a call at a primary station to be switched to a secondary station. Also, in this type of system, additional per station relay equipment is utilized to enable telephone stations not assigned to a controller to be in a pick-up group controlled by that controller.
While the above system reduces the processing constraints on the centrex exchange and allows for use of digital telephone stations, the switching equipment needed in each controller is complex and costly. Furthermore, as the number of stations in the pick-up groups increases, the ability of this type of system to meet these demands becomes more difficult.
It is, therefore, a primary object of the present invention to provide an improved centrex exchange with multi-station pick-up capability.
It is a further object of the present invention to provide a centrex exchange with a versatile multi-station pick-up capability in a way which does not substantially reduce the centrex exchange capacity.
It is a further object of the present invention to provide a modular station controller for a centrex exchange meeting the above objects.